1. Field of the Invention
The invention relates in general to an active matrix organic light emitting diode (OLED) pixel unit, and more particularly to an active matrix OLED pixel unit applied in a liquid crystal display.
2. Description of the Related Art
FIG. 1 is a circuit diagram of a conventional active matrix OLED pixel unit. Referring to FIG. 1, the pixel unit includes a first switch 104, a second switch 106, a first transistor 105, a second transistor 108, a capacitor 107 and an OLED 109.
The first switch 104 has its control end for receiving a first scan signal SC1, its first end for receiving a data signal DT1 and its second end coupled to a second end of a first transistor 105. The first transistor 105 has its first end coupled to a positive voltage, its control end coupled to its second end and a first end of the second switch 106. The second switch 106 has its control end for receiving a second scan signal SC2 and its second end coupled to a control end of the second transistor 108. The second transistor has its first end coupled to the positive voltage and its second end coupled to an anode of the OLED 109. The cathode of the OLED 109 is coupled to a ground. The capacitor 107 is coupled between the positive voltage and the control end of the second transistor 108.
When the first scan signal SC1 and the second scan signal SC2 are enabled, the switches 104 and 106 are turned on to charge the capacitor 107 and a current corresponding to the data signal DT1 flows through the transistor 105. When the switch 106 is turned on, the transistors 105 and 108 form a current mirror structure such that the current corresponding to the data signal DT1 flows through the transistor 108 to generate a corresponding luminance of the OLED. When the first scan signal SC1 and the second scan signal SC2 are disabled, the switches 104 and 106 are turned off. The voltage drop across the capacitor 107 is unchanged, the transistor 108 remains to have the same current and thus the OLED 109 is still turned on.
According to the above design, the conventional structure of active matrix OLED pixel unit is still lack of design variety in manufacturing process when the extra wiring layout is needed to achieve a better electrical property.